Unable to connect to my server

Good evening! I've just registered my account and created a server. I wanted to play Attack of the B-Team (by Technic) and it worked just once after refreshing over and over for around 5 minutes. I disconnected from the server and 3 hours later, I couldn't log in anymore. I tried to refresh but it doesn't work. It says that my launcher has to be in 1.13 or 1.15.1 (2 versions, it depends of how often I refresh).

Since it worked once, I think the IP is correct. What's the DynIP ?

It works with the normal IP and the DynIP. I have absolutely no idea why it is working now but not yesterday. I hope it will still work tomorrow... Thank you anyway for your answers and your help.

I've got a new problem now: when I log in, my character falls out of the world on my screen but is actually not moving on the surface...

Nevermind, I'm just lagging a lot on this server... But my friends don't.